Getting logical path from Perl?

mathomp4 has asked for the wisdom of the Perl Monks concerning the following question:

I am most definitely not a Perl guru, so I might be asking a simple question but...I can't figure it out. I work on a model that uses Perl for some scripting that creates other scripts. I also work on a system where directories can "move" because of NFS. As an example, I have a directory on the system:

/discover/nobackup/mathomp4

That is actually a path through a symlink:

$ pwd -L
/discover/nobackup/mathomp4
$ pwd -P
/gpfsm/dnb44/mathomp4
[download]

Every so often, due to disk systems filling up, they might have to move us from, say, dnb44 to dnb45, and if I use Perl to make a script before that move, well, things break. So, it would be good for Perl to use the logical and not physical path. For example, I have a script that wants to know what directory it was called from. My hope after reading the FindBin docs:

$Bin         - path to bin directory from where script was invoked
$RealBin     - $Bin with all links resolved
[download]

was that Bin would do it, but it seems to be the same as RealBin:

$ cd $HOME
$ cat /discover/nobackup/mathomp4/MyTestScript/bin/test.pl
#!/usr/bin/env perl
use FindBin;
use File::Basename;
my $fvroot = dirname($FindBin::Bin);
print "Using Bin:     $fvroot\n";
my $fvroot2 = dirname($FindBin::RealBin);
print "Using RealBin: $fvroot2\n";
$ /discover/nobackup/mathomp4/MyTestScript/bin/test.pl
Using Bin:     /gpfsm/dnb44/mathomp4/MyTestScript
Using RealBin: /gpfsm/dnb44/mathomp4/MyTestScript
[download]

Dang. So is there any way for Perl to see the logical path rather than the physical one?

Comment on Getting logical path from Perl? Select or Download Code

Replies are listed 'Best First'.
Re: Getting logical path from Perl? by hippo (Bishop) on Mar 08, 2021 at 13:59 UTC
Does this do what you want? `$ cat /tmp/foo/mydir.pl #!/usr/bin/env perl use strict; use warnings; use Path::Tiny; my $path = path ($0); my $dir = $path->parent->stringify; print "\$0: $0\n"; print "Path::Tiny: $dir\n"; $ ls -l /tmp/foo lrwxrwxrwx. 1 user users 3 Mar 8 13:47 /tmp/foo -> bar $ /tmp/foo/mydir.pl $0: /tmp/foo/mydir.pl Path::Tiny: /tmp/foo $` [download] 🦛	[reply] [d/l]
Re^2: Getting logical path from Perl? by mathomp4 (Novice) on Mar 09, 2021 at 13:20 UTC
Good news, it does what we want. Bad news, it depends on the calling script using the logical path to the script, which might expose the same issue. I'm beginning to think we might just need to rewrite some scripting to be more robust... That said, thanks for all the lessons in Perl!	[reply]
Re: Getting logical path from Perl? by Tux (Canon) on Mar 08, 2021 at 15:47 UTC
I interpret the question as : I only want to run this script if it is invoked from the symlinked folder. Use Path::Tiny if you want to stay portable (as posted earlier). Check `-l`, `readlink`, and `Cwd::abs_path` to fill your needs. `#!perl use Cwd qw( getcwd abs_path ); my ($DIR, $CMD) = $0 =~ m{^(.*)/([^/]+)$}; ! $CMD && ! -d $DIR and ($DIR, $CMD) = (getcwd, $DIR); # "." in $PATH +and script invoked without ./ -l $DIR or die "$DIR is not the symlinked folder. Running like this is + dangerous!\n"; say "Current dir : ", getcwd; say "Invoking folder: ", $DIR; say "Symlink : ", readlink $DIR; say "Abs path: : ", abs_path $DIR;` [download] `$ mkdir -p tmp/test-a $ ln -s test-a tmp/test $ ln -s tmp/test test $ vi tmp/test/test.pl -- paste above code and save $ perl test/test.pl Current dir : /home/tux Invoking folder: test Symlink : tmp/test Abs path: : /home/tux/tmp/test-a` [download] Enjoy, Have FUN! H.Merijn	[reply] [d/l] [select]
Re: Getting logical path from Perl? by talexb (Chancellor) on Mar 08, 2021 at 13:54 UTC
If `pwd -L` gives you the answer you want, can you just grab that value when you need it? Alex / talexb / Toronto Thanks PJ. We owe you so much. Groklaw -- RIP -- 2003 to 2013.	[reply] [d/l]
Re^2: Getting logical path from Perl? by mathomp4 (Novice) on Mar 08, 2021 at 17:59 UTC
The issue with `pwd -L` is that we don't always run these scripts from the bindir. So, we'd have to `chdir` to do so and: $ cat /discover/nobackup/mathomp4/MyTestScript/bin/test-pwd.pl #!/usr/bin/env perl use FindBin; use File::Basename; my $fvroot = dirname($FindBin::Bin); print "Using Bin: $fvroot\n"; my $fvroot2 = dirname($FindBin::RealBin); print "Using RealBin: $fvroot2\n"; chomp($pwdL = `pwd -L`); print "Current pwd -L: $pwdL\n"; chdir($fvroot); chomp($pwdL2 = `pwd -L`); print "After pwd -L: $pwdL2\n" $ /discover/nobackup/mathomp4/MyTestScript/bin/test-pwd.pl Using Bin: /gpfsm/dnb44/mathomp4/MyTestScript Using RealBin: /gpfsm/dnb44/mathomp4/MyTestScript Current pwd -L: /home/mathomp4 After pwd -L: /gpfsm/dnb44/mathomp4/MyTestScript [download] So, it's not logical because the chdir didn't go to the logical path! That said, I haven't yet tested the Path::Tiny yet.	[reply] [d/l] [select]


Perl-Sensitive Sunglasses
	PerlMonks